The present invention relates to a method for connecting a ground circuit width an electromagnetic wave shielding layer of a printed wiring circuit in a printed circuit board having an electromagnetic wave shielding layer.
In a conventional printed circuit board, in order to avoid the circuit from malfunctioning between printed wiring circuits or external apparatus due to electromagnetic interference, it is proposed to shield the entire surface or the local portion of the above-mentioned printed wiring circuit by providing an electromagnetic wave shielding layer on the upper side of the printed wiring circuit via an insulating layer.
The electromagnetic wave shielding layer and the ground circuit of the printed wiring circuit is connected in the printed circuit board as shown in FIG. 2. That is, when an insulating layer 3 is formed on the upper side of a printed wiring circuit 2 formed on the whole surface of a base material board 1, a ground circuit terminal portion (hereinafter referred to as a ground terminal) 4 of the printed wiring circuit 2 has bored through its upper side a connecting portion (hereinafter referred to as a terminal) 5 whose aperture is the same as the aperture of the ground terminal 4. Thereafter, the connecting terminal 5 is formed to electrically connect an electromagnetic wave shielding layer 6 and the ground terminal 4 by a conductive material filled into the terminal 5 when the electromagnetic wave shielding layer 6 is formed on the upper side of the above-mentioned insulating layer 3. Then, the electromagnetic wave shielding layer 6 and the printed wiring circuit 2 are electrically connected by the connecting terminal 5.
While the electromagnetic wave shielding layer 6 and the ground terminal 4 are connected in the printed circuit board 7 through the connecting terminal 5 which is formed at the same time when the electromagnetic wave shielding layer 6 is formed, the electromagnetic wave shielding layer 6 is generally formed by coating a conductive paste by a silk screen printing process. There are then disadvantages because an electrical connection of the terminal 5 becomes defective and that the stability of the connecting of the terminal 5 becomes irregular.
More specifically, the area of the concave or recess portion of the connecting terminal 5 between the insulating layer 3 and the ground terminal 4 formed on the upper side of the printed wiring circuit 2 is limited and becomes a small space in accordance with the increased density of the wiring circuit. Thus, when the conductive paste is coated in the forming process of the electromagnetic wave shielding layer 6, the conductive paste is not smoothly filled into the connecting terminal 5 resulting in the formation of bubbles. Also, the edge of the opening portion hinders the conductive paste from being smoothly filled into the connecting terminal 5 which may result in an incomplete connection. As a consequence, a stable connection with the terminal 5 cannot be obtained.